1. Field of the Invention
The present invention relates to a technique for polishing, for example, one side of a semiconductor wafer.
2. Description of the Related Art
As a conventional apparatus for polishing one side of a work such as a semiconductor wafer, there is known an apparatus equipped with a work holding plate made of metal, ceramics, glass or the like attached to a rotary holder which can be rotated, and a polishing pad attached on a polishing turn table which can be rotated. One side of the work is held on a work holding surface of the work holding plate, and the other side of the work is contacted and rubbed with the polishing pad with providing polishing agent to the surface which is contacted and rubbed, and thereby a surface of a work is polished.
As a method for holding the work on the work holding surface, a method of holding a work by fixing it directly on the surface using, for example, adhesive, wax or the like, a method of vacuum-holding using porous ceramics or the like are known. A technique of forming a resin layer on the work holding surface is also known, as disclosed in, for example Japanese Patent Publication No. 63-4937.
A polishing pad having viscoelastic properties is deformed during polishing. In order to correct degradation of flatness due to the deformation and improve flatness of a work, especially a thin work such as a wafer, Japanese Patent Application Laid-open (kokai) No. 63-318260 proposes a method comprising deforming the polishing pad using a dummy work so as to be in the same condition as the condition when polishing a work to be treated, thereafter polishing the work holding surface of the work holding plate with the deformed polishing pad so as to conform with the shape of the deformed polishing pad, namely, co-rubbing polishing (hereinafter referred to as xe2x80x9cwork holding surface optimization polishingxe2x80x9d), then holding one side of the work with the work holding surface subjected to work holding surface optimization polishing, and subsequently polishing the other side of the work.
There are also known a method of increasing polishing load of a dummy work to accelerate deforming rate of a polishing pad in order to efficiently polish a work holding surface to be subjected to work holding surface optimization polishing as disclosed in Japanese Patent Application Laid-open (kokai) No. 4-242929, and a method of previously forming an acrylic resin layer or a polycarbonate resin layer on the work holding surface of the work holding plate, and subjecting the resin layer to work holding surface optimization polishing. Using the resin layer enables work holding surface optimization polishing can be conducted in short time, and the back side of the work can be protected.
Work holding surface optimization polishing disclosed in Japanese Patent Application Laid-open (kokai) No. 63-318260 is considered to be effective technique for flattening process. However, if the temperature of the work holding surface when polishing work holding plate directly is different from the temperature of the work holding surface when polishing the work, it causes degradation of flatness.
Namely, heat generated at a polishing portion makes difference between the temperature of the work holding surface on the top side of the plate and the temperature of the surface on the back side of the plate, which causes deformation of the work holding plate. When the temperature of heat generated during work holding surface optimization polishing and the temperature of heat generated during polishing the work are different, the deformation amount of the work holding plate due to heat generated during work holding surface optimization polishing will be different from the deformation amount of the work holding plate due to heat generated during polishing the work, and it causes degradation of flatness.
In the technique wherein a resin layer is formed on a work holding surface, when an acrylic resin is used, a processing speed of work holding surface optimization polishing can be accelerated so that processing time therefor can be shortened. However, because of low rigidity, when the resin layer which is adhered on the holding plate is polished to be too thin, non-uniformity of adhesion is caused, which is undesirable by reason that, for example, the non-uniformity of adhesion is transferred to the processing surface of the work held thereon.
On the other hand, if the resin layer is too thick, rigidity of the work holding surface will be insufficient, which may cause problems such as unstable flatness on processing the work, generation of a crack in the resin layer due to the difference of the thermal expansion coefficient of the resin and the holding plate, and the like.
When polycarbonate is used for the resin layer, as it has higher rigidity than an acrylic resin, it does not cause a problem of degradation of flatness due to insufficient rigidity or the like. However, friction resistance in work holding surface optimization polishing will be large, load on the polishing apparatus will be high, and therefore stable polishing will be difficult.
Moreover, when polycarbonate is used, processing speed will be low, resulting in longer processing time, larger heat release amount, which causes a problem that a deformation degree of the work holding plate due to heat is unstable.
The present invention has been accomplished to solve the above-mentioned problems, and an object of the present invention is to achieve stable work flatness by eliminating difference of thermal effect when conducting work holding surface optimization polishing and when polishing a work, and give a good influence on work flatness by using an appropriate material for a resin layer formed on the work holding surface in a method of processing comprising subjecting the work holding surface of the work holding plate to work holding surface optimization polishing to conform with the deformed shape of a polishing pad, holding a work with the work holding surface subjected to work holding surface optimization polishing, and polishing the work.
To achieve the above object, the present invention provides a method of polishing a work comprising polishing a work holding surface by contacting and rubbing a work holding plate with a polishing pad (work holding surface optimization polishing), holding a back surface of the work on said work holding surface of said work holding plate, and thereafter contacting and rubbing the work with said polishing pad to polish the front surface of the work characterized in that a temperature of said work holding surface of said work holding plate when polishing said work holding surface (work holding surface optimization polishing) and a temperature of said work holding surface of said work holding plate when polishing the work are controlled to be the same.
According to the above method, degradation of flatness can be prevented by controlling the temperature when conducting work holding surface optimization polishing and the temperature when polishing a work to be the same to eliminate the difference of the deformation amount of the work holding plate due to heat generated during work holding surface optimization polishing and during polishing the work.
In an embodiment of the present invention, the temperature of said work holding surface can be controlled by controlling a temperature of polishing agent provided during polishing, or by controlling a temperature of a polishing turn table holding the polishing pad, or by controlling both of them.
The temperature of the work holding surface when conducting work holding surface optimization polishing and temperature of the work holding surface when polishing the work are controlled to be the same by controlling a temperature of polishing agent and/or a polishing turn table holding the polishing pad as described above.
The temperature of the polishing agent and the polishing turn table can be controlled using a temperature controller provided in at least one of a polishing agent supplying system and a polishing turn table. The temperature of the polishing turn table can be controlled easily by, for example, controlling temperature of cooling water for cooling the polishing turn table.
Control of the temperature can be conducted either by controlling the temperature when conducting work holding surface optimization polishing to be the same as the temperature when polishing the work, or by controlling the temperature when polishing the work to be the same as the temperature when conducting work holding surface optimization polishing. It can also be conducted by controlling both of them to be a certain temperature.
In an embodiment of the present invention, a resin layer may be formed on the work holding surface of the work holding plate, and pores for vacuum-holding may be formed in the resin layer and the work holding plate.
When the resin layer is formed on the work holding surface as described above, the processing when conducting work holding surface optimization polishing can be conducted easily, dirt on the back side of the work is hardly adhered on the work holding surface so that stable processing accuracy can be achieved, and furthermore, the back side of the work can be held softly so that the work can be protected well.
The resin layer can be formed by adhesion of the resin plate or resin coating by any other method.
In an embodiment of the present invention, the resin layer is formed of ABS resin or epoxy resin.
ABS (acrylonitrile butadiene styrene copolymer) resin and epoxy resin are excellent in workability, processing time for work holding surface optimization polishing will be short, and heat release amount during work holding surface optimization polishing will be stable so that the temperature can be controlled accurately and easily. Moreover, the resins show relatively high rigidity when holding the work so that the work can be polished in high accuracy.
In an embodiment of the present invention, thickness of the resin layer may be in the range of 1 to 5 mm.
When the resin layer is formed in the range of thickness, work flatness can be improved.
Namely, thickness less than 1 mm may lead to the problem that non-uniformity of adhesion is transferred to the processing surface of the work held thereon. Thickness more than 5 mm may lead to lower rigidity for holding the work, resulting in unstable work flatness.
As explained above, according to the present invention, a temperature of the work holding surface when work holding surface optimization polishing and a temperature of the work holding surface when polishing the work are controlled to be the same in the method of polishing the work comprising subjecting a work holding plate to work holding surface optimization polishing, holding the work on the work holding surface thereof, and contacting and rubbing the work with the polishing pad for polishing, and thus the difference of the deformation amount of the work holding plate due to heat is eliminated so that flatness of the work can be improved.
In the method, when the temperature of said work holding surface is controlled by controlling a temperature of polishing agent, or by controlling a temperature of a polishing turn table holding the polishing pad, or controlling both of them, and a temperature controller is provided in at least one of the polishing agent supplying system and the polishing turn table, control of the temperature can be conducted easily.
When a resin layer is formed on the work holding surface, the processing when conducting work holding surface optimization polishing can be conducted easily, dirt on the back side of the work is hardly adhered on the work holding surface so that stable processing accuracy can be achieved, and furthermore, the back side of the work can be held softly so that the work can be protected well.
When the resin layer is formed of the predetermined resin, work holding surface optimization polishing can be conducted in short time as the resins are excellent in workability. Moreover, when the resin is used, heat release amount generated during work holding surface optimization polishing will be stable so that temperature can be controlled accurately and easily. Moreover, the resins show relatively high rigidity when holding the work so that the work can be polished in high accuracy.
When thickness of the resin layer is in the predetermined range, work flatness can be further improved.